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Unformatted text preview: 1 ENERGY BANDS ENERGY BANDS Sections 2.12.7 of course text: 1. Primitive unit cell 2. Periodic potential 3. Bloch's Theorem 4. Energy bands 5. Reducedzone plot 6. Bragg reflection 7. Quantum states 8. Material classification 2 Primitive unit cell Primitive unit cell How many atoms/cc are there in Si? 5E22 Instead of dealing with such huge numbers, we capture the structural essence in the Primitive Unit Cell. What are the primitive unit cells for the following structures? Which two of these structures have a BASIS of 2? 3 Periodic potential Periodic potential 1D periodic array of primitive cells, each containing 1 monovalent atom. 1D Coulombic potential for an array of primitive cells Squarewell representation Deltafunction representation Any periodic potential will do for our purpose of revealing and BANDGAPS ENERGY BANDS 4 Setting up the problem to solve Setting up the problem to solve for the allowed energies for the allowed energies Electron PE [ ] U E m g − = 2 2 2 h Write SWE as: For 0 < x < a General solution Boundary conditions 5...
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 Fall '09
 David
 Condensed matter physics, Bloch wave, 2. 3. 4. 5. 6. 7. 8, primitive unit cell

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